A) Structural studies of human erythrocyte membrane sialoglycoprotein concern 1) detailed structure and disposition of the oligosaccharide unit(s) 2) heterogeneity of carbohydrate composition, number of oligosaccharide units per mole of glycoprotein, degree of carbohydration and disposition of units in preparations of individual donors. 3) Isolation and characterization of three CNBr peptides. B) Structural studies of cell surfaces of WI38 diploid human lung fibroblasts - concern isolation and characterization of surface tryptic peptides as a function of "age" in culture. Cells labelled to constant specific activity with (UC14) glucose are used and the focus is on carbohydrate composition, and type, number and structure of oligosaccharide units.